The present invention concerns an electromagnetic actuation device.
Such a device is, for example, of known art from DE 198 48 919 A1 as an electromagnetic valve device. As a reaction to the energisation of a (stationary) coil unit, an armature unit, guided in a radially symmetrical manner in the interior of the coil, moves and opens or closes a valve seat for the fluid that is to be controlled.
Here the armature unit (essentially having a cylindrical armature body) moves along the axial direction relative to a stationary core unit, which is part of the magnetic circuit, and which by means of its configuration influences the movement characteristic, in particular a magnetic armature force of the armature unit. In concrete terms the device cited as prior art features a so-called control cone region (control region) for purposes of influencing the movement characteristic, i.e. the force profile, of the armature movement in the crossover region between the (movable) armature unit and the (stationary) core unit; the said control cone region influences the magnetic flux in the magnetic circuit between armature unit, core unit, and the other magnetic circuit elements that are involved, along the axial direction, in a region of the armature stroke (namely the region immediately after the release of the armature unit from the core unit).
The control cone of known art from DE 198 48 919 A1, here in the form of an annular step, running around the periphery of the armature end face, and flattened outboard, and a corresponding (radial) inner form on the side of the core unit, here effects, for example, an increase of the magnetic force of the armature in the initial stroke region described. As a result of the overlap shown between the armature unit and the core region the necessary magnetomotive force of core and armature reduces as a result of energisation of the coil, relative to that for a so-called flat cone, namely a configuration of the crossover region between armature unit and core unit with no axial overlap, i.e. with no reduction of the working air gap. Accordingly the magnetic field lines of the magnetic flux over the axial overlap are primarily closed, as a consequence of which the magnetic force in this armature initial stroke region is specifically increased.
By means of a suitable configuration of the said control region (control cone region), for example, specification of an effective axial overlap, it is possible to influence specifically the movement characteristic of the armature unit, in particular a profile of the magnetic force along the movement stroke (movement stroke path); to reinforce or weaken, for example, the profile comparatively or point-by-point.
However, the axial overlap of armature unit and control unit in the control region, which is to be taken to be of known art, also brings with it potential disadvantages, in particular in terms of the wear and service life properties of electromagnetic actuation devices configured in this manner. Thus in particular, as a result of the axial overlap of the profile sections on the armature and core forming the control region, in addition to the axial magnetic flux profile that is important for the armature movement, there also arises a radial component (i.e. a component normal to the axial direction) of the magnetic flux profile, across the air gap formed between the facing walls of the profile sections. The said magnetic force component (which is radial in radially symmetrical arrangements) causes disadvantageous transverse forces, which have a disadvantageous effect in practice, i.e. in particular in conjunction with frequent movement cycles, or long operating times. It is true to say that if the armature and core were to be exactly aligned relative to one another, the transverse force generated by the radial magnetic force component would be cancelled out in the centre and thus compensation would be effected. However, this cannot be achieved in practice, either in production, or in operation. Instead the effect can be observed that the armature unit (necessarily mounted with a radial clearance) within a surrounding guide has a tendency to tilt (within the bounds of the clearance that is present), whereby such an effect is, for example, additionally reinforced by compression springs that are not engaging quite centrally with the armature unit, or similar influences; production tolerances and other effects also play a role.
An armature unit of this kind, sitting within the bounds of the clearance fit in an inclined manner in the armature guide (in the form of a diametrical two-point contact on corresponding internal positions of the armature guide) leads firstly to the fact that core unit and armature unit (and consequently the profile sections forming the control region) are no longer exactly aligned, thus large radial air gaps of various sizes (more specifically: sectors of a peripheral air gap) appear around the periphery.
With energisation of the coil unit and the magnetomotive force in the control region thereby caused large magnetic transverse forces of unequal size accordingly arise in the air gap positions of various widths. Small radial air gaps generate relatively high magnetic transverse forces, while large radial air gaps correspondingly generate small magnetic transverse forces. These no longer compensate for each other in the radial direction, so that a resultant (radial) transverse force is formed in the direction of the smallest air gap.
This acts on the armature unit (mounted with clearance) as a normal force and generates static and sliding friction forces in accordance with the frictional values of the tribological system comprising the armature unit (or an armature sliding coating provided on the armature unit) and also the armature guide.
In the first instance these act negatively on the force balance of the magnet and lead to an (unnecessary) increase in the magnetic force requirement, and consequently to a larger magnet installation space.
In electromagnetic switching devices with a high service life requirement (typically more than 100 million switching cycles) the high magnetic transverse forces (normal forces) described also generate a disadvantageously high surface pressure onto the friction partners, and thereby accelerate their tribological wear. This is particularly serious, for example, in the case of pneumatic actuation applications (such as, for example, a pneumatic valve) since here no lubrication or similar can act so as to reduce the wear.
The consequence is premature failure, in particular in the case of systems with a control cone region optimised in terms of build size and energy consumption, in particular if the armature unit, in a manner otherwise of known art, is provided with sliding coatings of PTFE or MoS2 and no sliding film (itself, however, again complex) is used for purposes of guiding the armature.
It is therefore the object of the present invention to improve an electromagnetic actuation device of the generic kind in terms of its operational and wear characteristics, in particular to reduce disadvantageous transverse, i.e. normal forces, which promote tilting of the armature unit, and thus within the context of systems having an axially overlapping control region to combine a beneficial magnetic movement characteristic and energy optimisation with protection against undesirable wear as a result of disadvantageous friction.